Liquid crystal display device and method of manufacturing that

ABSTRACT

A liquid crystal display device includes a first substrate, a first alignment film formed over the first substrate, a second substrate, a second alignment film formed over the second substrate, a liquid crystal layer sandwiched between the first alignment film and the second alignment film, and a projecting portion formed over the second substrate. The first alignment film is a photo alignment film, and a thickness “d 2 ” of the second alignment film over the projecting portion and a film thickness “d 1 ” of a portion of the first alignment film facing the projecting portion satisfy formula (1) and (2):
 
0 nm&lt;d2&lt;30 nm  (1);
 
d2&lt;d1  (2).

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/872,451, filed Apr. 29, 2013, now U.S. Pat. No. 8,749,741, which is acontinuation of U.S. application Ser. No. 13/571,969, filed Aug. 10,2012, now U.S. Pat. No. 8,432,517, which is a continuation of U.S.application Ser. No. 13/230,252, filed Sep. 12, 2011, now U.S. Pat. No.8,243,240, which is a continuation of U.S. application Ser. No.12/962,128, filed Dec. 7, 2010, now U.S. Pat. No. 8,040,478, which is acontinuation of U.S. application Ser. No. 12/470,500, filed May 22,2009, now U.S. Pat. No. 7,859,625, the contents of which areincorporated herein by reference. This application also relates to U.S.application Ser. No. 13/571,930, filed Aug. 10, 2012, now U.S. Pat No.8,351,003, which is a continuation of U.S. application Ser, No.13/230,252, filed Sep. 12, 2011, now U.S. Pat. No. 8,243,240.

CLAIM OF PRIORITY

The present application claims priority from Japanese application serialNo. 2008-133840, filed on May 22, 2008, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device and amanufacturing method thereof, and more particularly to a liquid crystaldisplay device to which an improvement of an alignment film is appliedand a manufacturing method thereof.

2. Description of the Related Art

A liquid crystal display device is a display device which adjusts aquantity of transmitting light from a light source by controlling thedirection of liquid crystal molecules with an electric field.

In a TN (Twisted Nematic) mode, an IPS (In-Plane Switching) mode, and aVA (Vertical Alignment) mode which are applied to many active matrixdisplay devices currently, it is necessary to create a stable alignmentstate and hence, it is necessary to form an alignment film on at leastone of opposedly-facing surfaces of a pair of substrates which sandwicha liquid crystal layer therebetween.

Particularly, in the TN mode and the IPS mode, in principle, it isnecessary to perform treatment which imparts an ability of controllingthe alignment in the fixed direction to at least one of opposedly-facingsurfaces of the pair of substrates. Further, in the VA mode, it may bepossible to control initial driving of the liquid crystal molecules byforming projections or stripes on at least one of opposedly-facingsurfaces of the pair of substrates. However, in forming theseprojections or stripes, there exists a possibility that the throughputis lowered at the time of forming the projections or the stripes. On theother hand, when neither projections nor stripes are formed, it isnecessary to impart an ability of controlling the alignment in theparticular direction with respect to an alignment film.

There may be a case where surface unevenness is provided to a backgroundof the alignment film. For example, the liquid crystal display deviceadopts the constitution in which spacers (hereinafter referred to aspillar-shaped spacers) are arranged on one of opposedly-facing surfacesof the pair of substrates in place of scattering bead spacers asseparate members, and spacer pedestals which are arranged to face thepillar-shaped spacers in an opposed manner are formed on anotheropposedly-facing surface.

To consider a case where an impact is applied to the liquid crystaldisplay device having such a constitution, when the spacer and thespacer pedestal are brought into contact with each other, an alignmentfilm on a surface of the spacer is abraded or peeled off thus givingrise to drawback that bright spots are generated thus causing a displaydefect.

A technique which can overcome this drawback is disclosed inJP-A-2000-267114 (patent document 1).

Patent document 1 states that the above-mentioned drawback can beovercome by making a film thickness of an alignment film on a topsurface of a spacer smaller than a film thickness of the alignment filmon portions other than the top surface of the spacer (or setting thefilm thickness of the alignment film on the top surface of the spacer tozero). In other words, the drawback can be overcome by applying analignment film material and, thereafter, by performing time-prolongedleveling corresponding to viscosity by prolonging a time for leveling.To be more specific, patent document 1 states “a solution containingpolyimide is applied by coating to the whole surface of a glasssubstrate on which pixel electrodes are formed by offset printing, acoated film is leveled for 60 seconds, and the leveled coated film isdried at a temperature of 100° C., and is baked at a temperature of 180°C. for 1 hour thus forming an alignment film having a thickness of 1000angstrom. Thereafter, rubbing treatment is applied to the alignmentfilm.” That is, due to (A): “leveling processing”, an organic solventcontaining the alignment film material arranged on an upper surface of aprojection is moved to a low place around the projection and hence, theorganic solvent is leveled. By prolonging this time, “local reduction offilm thickness” of the alignment film on the projection can be realized.Further, due to (B): “baking process”, the organic solvent is evaporatedso that “the reduction of film thickness at a fixed ratio over the wholesurface” of the alignment film can be realized. With respect to thealignment film to which rubbing treatment is applied, the film thicknessof the whole alignment film is substantially determined through thesetwo reduction-of-film-thickness processes.

SUMMARY OF THE INVENTION

In the method disclosed in patent document 1, the projection whichconstitutes the spacer is sufficiently high, that is, a height of thespacer is 2 to 3 μm and hence, the alignment film is formed such thatthe leveling of the film can be realized by performing leveling forapproximately 60 seconds, thus forming the alignment film such that onlythe alignment film having a thickness of approximately several nmremains on the upper surface of the spacer. However, when a pedestalwhich is smaller and lower than the spacer is adopted as the spacerpedestal, a display defect occurs even when the structure disclosed inpatent document 1 is adopted.

Accordingly, it is an object of the present invention to provide aliquid crystal display device which can eliminate such a display defect.

Inventors of the present invention, upon analysis of a mode of theabove-mentioned display defect, arrived at an idea that the displaydefect is caused not only by the alignment film on the pillar-shapedspacer but also by the alignment film on the spacer pedestal.

Accordingly, the inventors of the present invention made an attempt tomake the alignment film thin by applying leveling (flattening) treatmentto the alignment film as in the case of the related art. However, thespacer pedestal arranged on an opposedly facing surface of thepillar-shaped spacer usually has a thickness of only approximately 0.5μm and hence, the film thickness of the alignment film on the spacerpedestal cannot be sufficiently decreased. To be more specific, althoughthe reduction of the film thickness of the alignment film also dependson viscosity, the film thickness of the alignment film on the spacerpedestal is reduced to only approximately 60 to 80% of the filmthickness of the alignment film of the pixel electrode.

Such a film thickness reducing operation still leaves the alignment filmhaving the large thickness on the spacer pedestal thus giving rise to adisplay defect which is caused by peeling of the alignment filmattributed to a contact between the pillar-shaped spacer and the spacerpedestal.

Inventors of the present invention then studied a method of increasing aheight of a spacer pedestal. The inventors of the present invention madean attempt to form the spacer pedestals by using only line layers andsilicon layers of transistors formed on an active matrix substrate onwhich the spacer pedestals are formed for forming the spacer pedestalsat a low cost. It is found difficult to form the spacer pedestals havinga height exceeding 1.0 μm without increasing the number of processes.Basically, the spacer pedestal having such a height is weak against animpact and hence, the spacer pedestal is not preferable as a spacerpedestal.

The inventors of the present invention, then, considered the formationof the alignment film having the small thickness as a whole bydecreasing a quantity of an organic solvent containing an alignment filmmaterial. However, such a method spends a considerable time in leveling,gives rise to surface irregularities on the alignment film formed on thepixel electrode and hence, there may be a case that the alignment filmon the pixel electrode cannot ensure a sufficient film thickness.

In this manner, the conventional approaches have suffered from therestriction in the manufacture of liquid crystal display devices.

As disclosed in JP-A-2005-351924 (patent document 2), inventors of thepresent invention studied the use of a photo alignment film as analignment film of an IPS type liquid crystal display device and arrivedat the following idea through studies on a photo-decomposition-typealignment film material. That is, the inventors of the present inventionparticularly considered that by forming an alignment film by printingand baking a volatile organic solvent containing aphoto-decomposition-type alignment film material, and by radiating apolarized ultra-violet rays to the alignment film under a hightemperature environment of approximately 200° C., the alignment film isevaporated in a moment that the alignment film is subject to photodecomposition so that a film thickness of the alignment film isdecreased.

Accordingly, inventors of the present invention manufactured a liquidcrystal display device in which a photo-decomposition-type photoalignment film is used as an alignment film of a liquid crystal displaydevice which forms pillar-shaped spacers on one of the pair ofsubstrates and spacer pedestals on another of the pair of substrates,and a linearly polarized light is radiated to the alignment film thusimparting an alignment control function to the liquid crystal displaydevice.

To be more specific, an organic solvent which uses an alignment filmmaterial having a skeleton formed of cyclobutane tetracarboxylicacid-diamine phenyl ether is printed on a layer above the spacerpedestals as an alignment film material, the organic solvent is left forleveling (A: “leveling process”), and, thereafter, the organic solventis dried and temporarily baked (B: “baking process). A film thickness ofthe alignment film is measured after such temporary baking. Then, apolarized light is radiated to the alignment film for imparting analignment control ability to the alignment film and, at the same time, adecomposed material is sublimed under a high-temperature environment ofapproximately 200° C. (C: “alignment imparting process”), and the filmthickness of the alignment film is again measured. As a result, it isfound that the thickness of the alignment film is reduced after baking.

That is, the inventors of the present invention have found thefollowing. In performing a control of the film thickness of thephoto-decomposition-type photo alignment film, and more particularly, acontrol of locally decreasing the film thickness of the photo alignmentfilm on the spacer pedestal using the spacer pedestal which is smallerand lower than the pillar-shaped spacer, it is necessary to control notonly the condition on (A) “leveling process” in which “the filmthickness is locally reduced” and the condition on (B) “baking process”in which the film thickness is reduced at a rate “a” per hour as in thecase of the alignment film to be rubbed but also a condition on (C)“alignment imparting process” in which the film thickness is reduced ata fixed quantity “b” per hour.

To be more specific, in the above-mentioned (A) “leveling process”, theinventors of the present invention formed, as the alignment film on thespacer pedestal, an alignment film using an organic solvent having thesame viscosity as the alignment film on the pillar-shaped spacer on acolor filter substrate side as described in the related art. However,the inventors of the present invention could not achieve the sufficientreduction of the film thickness. This is attributed to a fact that thespacer pedestal is lower than the pillar-shaped spacer and hence, theremay be a case that, in the adjustment of viscosity of the organicsolvent for the alignment film on the pillar-shaped spacer, theviscosity is so high that the sufficient leveling cannot be performed.Accordingly, inventors of the present invention newly sought for aviscosity range of a volatile organic solvent containing an alignmentfilm material to be printed. As a result, the inventors of the presentinvention have found that a volatile organic solvent having viscosity of35 Pa·s or less which contains a photo-decomposition-type alignment filmmaterial is necessary.

In the related art, in (A) “leveling” and (B) “baking process”, when theviscosity of the organic solvent is adjusted for forming thepillar-shaped spacer, the relationship of film thickness of alignmentfilm on the spacer pedestal/the film thickness of the alignment film onthe pixel electrode is set to approximately 60 nm/120 nm, while when theviscosity of the organic solvent is adjusted for forming the spacerpedestal, the film thickness can be reduced to an extent that therelationship becomes approximately 30 nm/120 nm.

Further, in (C) “alignment imparting process” found by the inventors ofthe present invention, the film thickness of the whole alignment filmcan be reduced by a fixed quantity and hence, the reduction of the filmthickness can be realized to an extent that the relationship of the filmthickness of the alignment film on the spacer pedestal/the filmthickness of alignment film on the pixel electrode becomes approximately10 to 15 nm/100 nm.

In this manner, the present invention realizes a novel task of “thedisplay defect attributed to “peeling of alignment film” generated on“the alignment film on the spacer pedestal”” which differs from “thealignment film on the pillar-shaped spacer” by a novel means whichcontrols the condition on (C) “alignment imparting processing” for newly“reducing the film thickness at a fixed quantity b/hour” besides (A)“leveling process” for “locally reducing the film thickness” and (B)“baking process”.

As a result, it is possible to, for the first time, realize a liquidcrystal display device in which a film thickness “d1” of aphoto-decomposition-type photo alignment film formed on the spacerpedestal (structure having an upper surface area smaller than thepillar-shaped spacer and being lower than the pillar-shaped spacer)satisfies a following formula 1.0 nm<d1≦30 nm  Formula 1

The thin alignment film formed on the spacer pedestal formed in thismanner is hardly peeled off or abraded. This result is brought about bya coupling agent which is added to the alignment film for enhancingadhesiveness of the alignment film with a background substrate. That is,it is considered that the alignment film is chemically coupled to abackground layer on an interface between the alignment film and thebackground layer due to the coupling agent so that the alignment filmclose to the background layer exhibits high adhesiveness, while theinfluence of the coupling agent is decreased along with the increase ofa distance from the background layer thus lowering the adhesiveness.Accordingly, it is considered that the thinner the formed alignment filmbecomes, the larger the adhesiveness of the alignment film is influencedby the coupling agent so that the adhesiveness is enhanced whereby theabrasion resistance of the alignment film at a portion thereof which isin contact with the pillar-shaped spacer is increased.

It must be noted that when the film thickness of the alignment film isextremely reduced over the whole surface of the spacer pedestal, aso-called pin hole phenomenon in which the alignment is not formedpartially is generated so that non-alignment portions are formed thusgiving rise to a display defect such as bright spots. Accordingly, it ispreferable to set a film thickness of the alignment film on a BM openingportion where the spacer pedestal is not arranged larger than the filmthickness of the alignment film at portions where the alignment film isin contact with the pillar-shaped spacer.

It is preferable to form a dedicated pattern for the spacer pedestalwithout arranging the spacer pedestal on the TFT element. The formationof the dedicated pattern reduces the possibility of generating physicaldamages or the deterioration of characteristics of existing parts.Further, the dedicated pattern can be formed without additionallyperforming a photolithography step when the dedicated pattern isarranged using the layered structure formed of the semiconductor layer,the gate electrode layer, the source electrode layer and the like whichconstitutes the TFT element and hence, the productivity is high.

The present invention is constituted as follows, for example.

(1) According to one aspect of the present invention, there is provideda manufacturing method of a liquid crystal display device which, forexample, includes: a pair of substrates; a liquid crystal layer which issandwiched between the pair of substrates; a first alignment film whichis formed on one of opposedly-facing surfaces of the pair of substrates;a second alignment film which is formed on another of opposedly-facingsurfaces of the pair of substrates; first projecting portions which areprovided to the first alignment film and project into the liquid crystallayer from first constitutional members which constitute a layer belowthe first alignment film; and second projecting portions which areprovided to the second alignment film, face the first projectingportions, and project into the liquid crystal layer by secondconstitutional members which constitute a layer below the secondalignment film, the first projecting portion being set lower than thesecond projecting portion, and an area of an upper surface of the firstprojecting portion is set smaller than an area of an upper surface ofthe second projecting portion, wherein the manufacturing method of aliquid crystal display device includes a first step of forming aphoto-decomposition-type polyimide film as the first alignment film bybaking a volatile organic solvent containing a photo-decomposition-typepolyimide acid having viscosity of not more than 35 mPa·s; and a secondstep of baking the polyimide film by radiating polarized lightcontaining ultraviolet rays to the polyimide film.

(2) In the above-mentioned manufacturing method of a liquid crystaldisplay device having the constitution (1), for example, themanufacturing method may further include a third step of forming aphoto-decomposition-type polyimide film as the second alignment film bybaking a volatile organic solvent containing a photo-decomposition-typepolyimide acid having viscosity of not more than 35 mPa·s; and a fourthstep of baking the polyimide film by radiating polarized lightcontaining ultraviolet rays to the polyimide film.

(3) In the above-mentioned manufacturing method of a liquid crystaldisplay device having the constitution (1), for example, one of the pairof substrates may include thin film transistors between the substrateand the first alignment film, and the first constitutional member mayinclude at least one of a semiconductor layer, a gate oxide film, a gateelectrode, an interlayer insulation film, a source electrode, and adrain electrode which constitute the thin film transistor.

(4) In the above-mentioned manufacturing method of a liquid crystaldisplay device having the constitution (3), for example, the liquidcrystal display device may include pixel electrodes each of which isconnected to one of the source electrode and the drain electrode of saidthin film transistor, and another substrate includes the counterelectrode.

(5) In the above-mentioned manufacturing method of a liquid crystaldisplay device having the constitution (1), for example, the firstprojecting portion may have a frusto-conical shape.

(6) According to another aspect of the present invention, there isprovided a liquid crystal display device which, for example, includes: apair of substrates; a liquid crystal layer which is sandwiched betweenthe pair of substrates; a first alignment film which is formed on one ofopposedly-facing surfaces of the pair of substrates; a second alignmentfilm which is formed on another of opposedly-facing surfaces of the pairof substrates; first projecting portions which are provided to the firstalignment film and project into the liquid crystal layer by firstconstitutional members which constitute a layer below the firstalignment film; and second projecting portions which are provided to thesecond alignment film, face the first projecting portions, and projectinto the liquid crystal layer by second constitutional members whichconstitute a layer below the second alignment film, the first projectingportion being set lower than the second projecting portion, and an areaof an upper surface of the first projecting portion being set smallerthan an area of an upper surface of the second projecting portion,wherein

the first alignment film is made of a photo-decomposition-type alignmentfilm material, and

a film thickness “d1” of the first alignment film on the firstprojecting portion and a film thickness “d2” of the second alignmentfilm on the second projecting portion satisfy a formula (1) and aformula (2).0 nm<d1<30 nm  (1)d2<d1  (2)

(7) In the above-mentioned liquid crystal display device having theconstitution (6), for example, the second alignment film may be made ofa photo-decomposition-type alignment film material.

(8) In the above-mentioned liquid crystal display device having theconstitution (6), for example, one of the pair of substrates may includethin film transistors between the substrate and the first alignmentfilm, and the first constitutional member may include at least one of asemiconductor layer, a gate oxide film, a gate electrode, an interlayerinsulation film, a source electrode, and a drain electrode whichconstitute the thin film transistor.

(9) In the above-mentioned liquid crystal display device having theconstitution (8), for example, the liquid crystal display device mayinclude pixel electrodes each of which is connected to one of the sourceelectrode and the drain electrode of each thin film transistor, andanother substrate includes the counter electrode.

(10) In the above-mentioned liquid crystal display device having theconstitution (6), for example, the first projecting portion may have afrusto-conical shape.

The above-mentioned constitutions are provided merely as examples andthe various modifications can be suitably made without departing from atechnical concept of the present invention. Further, constitutionalexamples of the present invention other than the above-mentionedconstitutions will become apparent from the whole description of thisspecification and drawings.

According to the liquid crystal display device and the manufacturingmethod thereof having the above-mentioned constitutions, the presentinvention can eliminate or reduce a display defect. Other advantageouseffects of the present invention will become apparent from the wholedescription of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an essential part showing anembodiment 1 of a liquid crystal display device according to the presentinvention;

FIG. 2 is a table showing constitutional members of the liquid crystaldisplay device shown in FIG. 1 and film thicknesses of theseconstitutional members;

FIG. 3 is a table showing the manufacture of alignment films in theliquid crystal display device shown in FIG. 1, and film thicknesses ofthe alignment films obtained by the manufacture;

FIG. 4 is a cross-sectional view of an essential part showing anembodiment 2 of a liquid crystal display device according to the presentinvention;

FIG. 5 is a table showing constitutional members of the liquid crystaldisplay device shown in FIG. 4 and film thicknesses of theseconstitutional members;

FIG. 6 is a table showing the manufacture of alignment films in theliquid crystal display device shown in FIG. 4, and film thicknesses ofthe alignment films obtained by the manufacture;

FIG. 7 is a cross-sectional view of an essential part showing anembodiment 3 of a liquid crystal display device according to the presentinvention;

FIG. 8 is a table showing the manufacture of alignment films in theliquid crystal display device shown in FIG. 7, and film thicknesses ofthe alignment films obtained by the manufacture;

FIG. 9 is a cross-sectional view of an essential part showing an exampleof a liquid crystal display device which constitutes a comparisonexample;

FIG. 10 is a table showing the manufacture of alignment films in theliquid crystal display device shown in FIG. 9, and film thicknesses ofthe alignment films obtained by the manufacture;

FIG. 11 is a table showing a bright-spot-generation withstand voltagelevel in the above-mentioned respective embodiments;

FIG. 12 is a table describing a content of references for determiningthe above-mentioned bright-spot-generation withstand voltage level; and

FIG. 13 is a view showing a graph which is obtained by converting thetable shown in FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are explained in conjunction withdrawings. In respective drawings and respective embodiments, theidentical or similar constitutional elements are given same symbols andtheir explanation is omitted.

<Embodiment 1>

(Constitution)

FIG. 1 shows a cross section of a liquid crystal display device (panel)of the present invention. FIG. 1 shows a portion of the liquid crystaldisplay device where a pillar-shaped spacer and a spacer pedestal areformed and a periphery of such a portion. FIG. 1 shows the constitutionof the liquid crystal display device corresponding to the examples 1 to4.

In FIG. 1, a so-called electrode substrate and a so-called countersubstrate are arranged to face each other in an opposed manner with aliquid crystal layer LC sandwiched therebetween.

The electrode substrate has following constitution, for example. Firstof all, the electrode substrate includes a substrate SUB1. On aliquid-crystal-layer-LC-side surface of the substrate SUB1, gateelectrodes GT and counter electrodes CT are formed. The gate electrodeGT constitutes a gate electrode of a thin film transistor TFT describedlater, and a scanning signal is supplied to the gate electrode GT from agate signal line not shown in the drawing. The counter electrode CT isan electrode which is provided for generating an electric field in theliquid crystal layer LC in corporation with a pixel electrode PXdescribed later. The counter electrode CT is a planar electrode formedof an ITO (Indium Tin Oxide) film, for example, which is formed over thesubstantially whole region of the pixel.

On a surface of the substrate SUB1, an insulation film GI is formed soas to also cover the gate electrodes GT and the counter electrodes CT.The gate insulation film GI functions as a gate insulation film in aregion where the thin film transistor TFT is formed.

A semiconductor layer AS is formed on the gate insulation film GI so asto overlap with the gate electrode GT, and a drain electrode SD and asource electrode SD are formed on an upper surface of the semiconductorlayer AS thus constituting a thin film transistor TFT. A video signal issupplied to one electrode out of the drain electrode SD and the sourceelectrode SD via a drain signal line not shown in the drawing. Further,another electrode out of the drain electrode SD and the source electrodeSD extends to the outside of a region where the thin film transistor TFTis formed, and is electrically connected with the pixel electrode PXdescribed later.

Then, in a region outside the region where the thin film transistor TFTis formed (for example, a region which overlaps with the gate signalline), a stacked body constituted of a semiconductor layer SC and ametal layer ML is formed. The semiconductor layer SC is formedsimultaneously with the formation of the semiconductor layer AS, whilethe metal layer ML is formed simultaneously with the formation of thedrain electrode SD and the source electrode SD. The stacked bodyconstituted of the semiconductor layer SC and the metal layer ML forms aspacer pedestal SS together with a protective film PAS described later.

On a surface of the substrate SUB1, the protective film PAS is formed soas to also cover the thin film transistor TFT and the stacked bodyconstituted of the semiconductor layer SC and the metal layer ML. Theprotective film PAS is provided for obviating a direct contact betweenthe thin film transistor TFT and the liquid crystal, and is formed of aninorganic insulation film, for example. On a portion of the protectivefilm PAS where the stacked body constituted of the semiconductor layerSC and the metal layer ML is formed, a projecting portion which projectsthan a periphery thereof is formed, and the projecting portion functionsas the spacer pedestal SS.

A pixel electrode PX which is constituted of a plurality of linearelectrodes arranged parallel to each other is formed on an upper surfaceof the protective film PAS in a region where the pixel electrode PXoverlaps with the counter electrode CT. The pixel electrode PX is formedof an ITO (Indium Tin Oxide) film, for example. The pixel electrode PXis electrically connected with another electrode out of the drainelectrode SD and the source electrode SD of the thin film transistor TFTvia a through hole formed in the protective film PAS at a position notshown in the drawing.

An alignment film ORI1 made of a photo-decomposition-type material isformed on a liquid-crystal-LC-side surface of the substrate SUB1 so asto also cover the pixel electrodes PX. The film thickness “b” of thealignment film ORI1 on a top surface of the spacer pedestal SS is setsmaller than the film thickness “a” of the alignment film ORI1 in aregion other than the top surface of the spacer pedestal SS (forexample, above the pixel electrode PX), or the film thickness “b” is setto zero. The film thickness “b” of the alignment film ORI1 on the topsurface of the spacer pedestal SS is set to a value of not more than 30nm. Here, the film thickness “a” of the alignment film ORI1 above thepixel electrode PX, for example, is set to 110 nm, for example. Amanufacturing method of the alignment film ORI1 is explained in detaillater.

On the other hand, the counter substrate is constituted as follows, forexample. First of all, a substrate SUB2 is provided. A black matrix BMand color filters FIL are formed on a liquid-crystal-LC-side surface ofthe substrate SUB2. The black matrix BM is formed between neighboringpixel regions, and the color filter FIL is formed so as to cover eachpixel region.

On an upper surface of the black matrix BM and upper surfaces of thecolor filters FIL, an overcoat film OC formed of a resin film, forexample, is formed. The overcoat film OC may be omitted in thisembodiment.

Pillar-shaped spacers PS are formed on an upper surface of the overcoatfilm OC at positions where the pillar-shaped spacers PS face the spacerpedestals SS in an opposed manner. The pillar-shaped spacer PS is formedwith a height and an area which are respectively larger than a heightand an area of the spacer pedestal SS. The pillar-shaped spacers PS areformed by selectively etching a resin film applied to the upper surfaceof the overcoat film OC by coating, and the pillar-shaped spacer PS hasa flat top surface.

Then, an alignment film ORI2 is formed on a liquid-crystal-LC-sidesurface of the substrate SUB2. The film thickness of the alignment filmORI2 on a top surface of the pillar-shaped spacer PS is set smaller thana film thickness “c” of the alignment film ORI2 in a region other thanthe top surface of the pillar-shaped spacer PS (for example, above theblack matrix BM), or the film thickness of the alignment film ORI2 onthe top surface of the pillar-shaped spacer PS is set to zero. Thereduction of the film thickness of the alignment film ORI2 on the topsurface of the pillar-shaped spacer can be realized by applying analignment film material to liquid-crystal-LC-side surface of thesubstrate SUB2 and, thereafter, by performing time-prolonged levelingcorresponding to viscosity by prolonging a leveling time.

With respect to the liquid crystal display device having suchconstitution, materials and film thicknesses of the above-mentionedrespective members are described in tables shown in FIG. 2. The uppertable shown in FIG. 2 describes the members on the counter substrate,wherein from a substrate SUB2 side to a liquid crystal layer LC side,sequentially, the black matrix BM (indicated by BM in the table), thecolor filter FIL (indicated by color pixel layer in the table), theovercoat film OC (indicated by overcoat in the table), the pillar-shapedspacer (indicated by pillar-shaped spacer in the table), and thealignment film ORI2 (indicated by alignment film (film thickness: “c”))are listed. Here, the film thickness of the alignment film ORI2indicates a film thickness at a portion where the film thickness is setto the film thickness “c” in FIG. 1, and a value of the film thicknessis described separately (see FIG. 3). The lower table shown in FIG. 2describes the members formed on the electrode substrate, wherein fromthe liquid crystal layer LC side to the substrate SUB1 side,sequentially, the alignment film ORI1 (indicated by alignment film (filmthickness: “a”) in the table), the pixel electrode PX (indicated bypixel electrode in the table), the protective film PAS (indicated byprotective film in the table), the source electrode and the drainelectrode (indicated by source/drain in the table), the semiconductordevice AS (indicated by a-Si in the table), the insulation film GI(indicated by gate insulation film in the table), the gate electrode(indicated by gate in the table), and the counter electrode (indicatedby common ITO in the table) are listed. Here, the film thickness of thealignment film ORI1 indicates a film thickness at a portion where thefilm thickness is set to the film thickness “a” in FIG. 1. The value ofthe film thickness is described separately (see FIG. 3).

(Manufacturing Method)

Next, one embodiment of a manufacturing method of the above-mentionedalignment film ORI1 and a manufacturing method of the alignment filmORI2 respectively is described. Although the explanation madehereinafter is directed to the manufacturing method of the alignmentfilm ORI1, the alignment film ORI2 is manufactured substantially in thesame manner.

First of all, an alignment film material is printed on the protectivefilm PAS formed on the electrode substrate by a printer, for example,such that the alignment film material also covers the spacer pedestalsSS. The alignment film material is made of a material having a skeletonformed of cyclobutane tetracarboxylic acid-diamine phenyl ether, forexample. Here, solution concentration and solution viscosity of thealignment film material are made different corresponding to a pluralityof examples. That is, as described in the table shown in FIG. 3,solution concentration and solution viscosity of the alignment filmmaterial are respectively set to 7 wt %, 30 mPa·s (example 1), 7 wt %,25 mPa·s (example 2), 8 wt %, 20 mPa·s (example 3), and 7 wt %, 35 mPa·s(example 4). Here, in all examples, solution viscosity is set to a valuesmaller than 35 mPa·s.

Then, the electrode substrate is heated on a hot plate at a temperatureof 80° C. for 3 minutes and, thereafter, is baked at a temperature of220° C. for 60 minutes. Here, the film thickness of the alignment filmmaterial at the portion where the film thickness assumes the filmthickness “a”, the portion where the film thickness assumes the filmthickness “b” and the portion where the film thickness assumes the filmthickness “c” in FIG. 1 is described for the above-mentioned respectiveexamples 1 to 4 in the table shown in FIG. 3 (item: before radiation oflight).

Thereafter, on the hot plate held at a temperature of 200° C., light(polarization light containing ultraviolet rays) generated by a lowpressure mercury lamp (integrated illuminance 5 mW/cm2 at 230 to 330 nm)is radiated for 1000 seconds (integrated radiation quantity: 5 J/cm2).Here, the film thickness of the alignment film material at the portionwhere the film thickness assumes the film thickness “a”, the portionwhere the film thickness assumes the film thickness “b” and the portionwhere the film thickness assumes the film thickness “c” in FIG. 1 isdescribed for the above-mentioned respective examples 1 to 4 in thetable shown in FIG. 3 (item: after radiation of light). As can beclearly understood from this table, in all embodiments, the filmthickness of the alignment film ORI1 on the top surface of the spacerpedestal SS can be set to a value of not more than 30 nm. That is, thefilm thickness of the alignment film ORI1 on the top surface of thespacer pedestal SS is set to 13 nm in the example 1, 10 nm in theexample 2, 8 nm in the example 3 and 30 nm in the example 4. On theother hand, the film thickness of the alignment film ORI1 in otherregion except for the top surface of the spacer pedestal SS (the regionabove the pixel electrode PX) is set to 110 nm in the example 1, 100 nmin the example 2, 110 nm in the example 3, and 120 nm in the example 4.

Further, the film thickness of the alignment film ORI2 on the countersubstrate side is set, at a portion in FIG. 1 where the film thicknessassumes the film thickness “c”, to 110 nm in the example 1, 100 nm inthe example 2, 110 nm in the example 3 and 120 nm in the example 4,while the film thickness of the alignment film ORI2 assumes a valuewhich is substantially zero on the top surface of the pillar-shapedspacer PS although not shown in FIG. 3.

In FIG. 3, for a comparison purpose, comparison examples 1 to 3 are alsodescribed. FIG. 3 shows a case where solution concentration and solutionviscosity of the alignment film material are respectively set to 6 wt %,50 mPa·s (comparison example 1), 5 wt %, 45 mPa·s (comparison example2), and 6 wt %, 40 mPa·s (comparison example 3), wherein solutionviscosity is set to a value larger than 35 mPa·s. In the table shown inFIG. 3, the film thickness of the alignment film before radiation oflight and the film thickness of the alignment film after radiation oflight are described in association with the above-mentioned examples.Here, it is found that the film thickness of the alignment film ORI1 onthe top surface of the spacer pedestal SS becomes larger than 30 nm.

<Embodiment 2>

(Constitution)

FIG. 4 shows the constitution of a liquid crystal display devicecorresponding to the examples 5 to 8, and corresponds to FIG. 1.

The constitution which makes the liquid crystal display device shown inFIG. 4 different from the liquid crystal display device shown in FIG. 1lies in that, first of all, the pillar-shaped spacers PS are formed onan electrode substrate side, and spacer pedestals SS are formed on thecounter electrode side. Further, the spacer pedestals SS are formed onan upper surface of an overcoat film OC as a resin layer, for example.

Also in this case, the film thickness “b” of an alignment film ORI2 on atop surface of the spacer pedestal SS is set smaller than a filmthickness “c” of the alignment film ORI2 in a region other than the topsurface of the spacer pedestal SS (for example, above a black matrixBM), or the film thickness “b” is set to zero. The film thickness “b” ofthe alignment film ORI2 on the top surface of the spacer pedestal SS isset to a value of not more than 30 nm. Here, the film thickness “c” ofthe alignment film ORI2 on the black matrix BM, for example, is set to110 nm, for example.

With respect to the liquid crystal display device having suchconstitution, materials and film thicknesses of the above-mentionedrespective members are described in tables shown in FIG. 5. The uppertable shown in FIG. 5 describes the members on the counter substrate,wherein from a substrate SUB2 side to a liquid crystal layer LC side,sequentially, the black matrix BM (indicated by BM in the table), thecolor filter FIL (indicated by color pixel layer in the table), theovercoat film OC (indicated by overcoat in the table), the spacerpedestal (indicated by pedestal in the table), and the alignment filmORI2 (indicated by alignment film (film thickness: “c”) in the table)are listed. Here, the film thickness of the alignment film ORI2indicates a film thickness at a portion where the film thickness is setto the film thickness “c” in FIG. 4. The value of the film thickness isdescribed separately (see FIG. 6). The lower table shown in FIG. 5describes the members formed on the electrode substrate, wherein fromthe liquid crystal layer LC side to the substrate SUB1 side,sequentially, the alignment film ORI1 (indicated by alignment film (filmthickness: “a”) in the table), the pillar-shaped spacer PS (indicated bypillar-shaped spacer in the table), the pixel electrode PX (indicated bypixel electrode in the table), the protective film PAS (indicated byprotective film in the table), the source electrode and the drainelectrode (indicated by source/drain in the table), the semiconductordevice AS (indicated by a-Si in the table), the insulation film GI(indicated by gate insulation film in the table), the gate electrode(indicated by gate in the table), and the counter electrode CT(indicated by common ITO in the table) are listed. Here, the filmthickness of the alignment film ORI1 indicates a film thickness at aportion where the film thickness is set to the film thickness “a” inFIG. 1. The value of the film thickness is described separately (seeFIG. 6).

(Manufacturing Method)

The manufacturing method of the alignment film ORI1 and themanufacturing method of the alignment film ORI2 are substantially equalto the corresponding manufacturing methods described in the embodiment1.

Solution concentration and solution viscosity of the alignment filmmaterial are made different corresponding to a plurality of examples.That is, as described in the table shown in FIG. 6, solutionconcentration and solution viscosity of the alignment film material arerespectively set to 7 wt %, 30 mPa·s (example 5), 7 wt %, 25 mPa·s(example 6), 8 wt %, 25 mPa·s (example 7), and 7 wt %, 35 mPa·s (example8). Here, in all examples, solution viscosity is set to a value smallerthan 35 mPa·s.

Here, the film thickness of the alignment film material at the portionwhere the film thickness assumes the film thickness “a”, the portionwhere the film thickness assumes the film thickness “b” and the portionwhere the film thickness assumes the film thickness “c” in FIG. 4 isdescribed for the above-mentioned respective examples 5 to 8 in thetable shown in FIG. 4 (item: after radiation of light). As can beclearly understood from this table, in all embodiments, the filmthickness of the alignment film ORI1 on the top surface of the spacerpedestal SS can be set to a value of not more than 30 nm. That is, thefilm thickness of the alignment film ORI1 on the top surface of thespacer pedestal SS is set to 13 nm in the example 5, 10 nm in theexample 6, 8 nm in the example 7 and 30 nm in the example 8. On theother hand, the film thickness “c” of the alignment film ORI2 in otherregion except for the top surface of the spacer pedestal SS (the regionabove the black matrix BM) is set to 110 nm in the example 5, 100 nm inthe example 6, 110 nm in the example 7, and 120 nm in the example 8.

Further, the film thickness of the alignment film ORI1 on the countersubstrate side is set, at a portion in FIG. 4 where the film thicknessassumes the film thickness “a”, to 110 nm in the example 5, 100 nm inthe example 6, 110 nm in the example 7 and 120 nm in the example 8,while the film thickness of the alignment film ORI1 assumes a valuewhich is approximately zero on the top surface of the pillar-shapedspacer PS although not shown in FIG. 6.

In FIG. 6, for a comparison purpose, comparison examples 4 to 6 are alsodescribed. FIG. 6 shows a case where solution concentration and solutionviscosity of the alignment film material are respectively set to 6 wt %,50 mPa·s (comparison example 4), 5 wt %, 45 mPa·s (comparison example5), and 6 wt %, 40 mPa·s (comparison example 6). In the table shown inFIG. 6, the film thickness of the alignment film before radiation oflight and the film thickness of the alignment film after radiation oflight are described in association with the above-mentioned examples.Here, it is found that the film thickness of the alignment film ORI1 onthe top surface of the spacer pedestal SS becomes larger than 30 nm.

<Embodiment 3>

(Constitution)

FIG. 7 shows the constitution of a liquid crystal display devicecorresponding to examples 9 to 11 and corresponds to FIG. 1.

The constitution which makes this embodiment different from theembodiment shown in FIG. 1 lies in that the spacer pedestal SS shown inFIG. 1 is not particularly necessary in this embodiment and a portionwhere a thin film transistor TFT is formed to function as a spacerpedestal. It is because that a drain electrode SD and a source electrodeSD of the thin film transistor TFT are formed as projecting portionshigher than a periphery of these portions and hence, these portions canbe also used as a spacer pedestal SS.

Also in this case, a film thickness “b” of an alignment film ORI1 on anupper surface of the thin film transistor TFT is set smaller than a filmthickness “a” of the alignment film ORI1 in a region other than theupper surface of the thin film transistor TFT (for example, above apixel electrode PX), or the film thickness “b” is set to zero. The filmthickness “b” of the alignment film ORI1 on the upper surface of thethin film transistor TFT is set to a value of not more than 30 nm. Here,the film thickness “a” of the alignment film ORI1 on the pixel electrodePX, for example, is set to 110 nm, for example.

In such constitution, materials and film thicknesses of respectivemembers of the embodiment 2 are substantially equal to the materials andthe film thicknesses of the respective corresponding members describedin the embodiment 1. That is, materials and film thicknesses ofrespective members have values substantially equal to values in thetable shown in FIG. 2.

(Manufacturing Method)

The manufacturing method of the alignment film ORI1 and themanufacturing method of the alignment film ORI2 are substantially equalto the corresponding manufacturing methods described in the embodiment1.

Solution concentration and solution viscosity of the alignment filmmaterial are made different corresponding to a plurality of examples.That is, as described in the table shown in FIG. 8, solutionconcentration and solution viscosity of the alignment film material arerespectively set to 7 wt %, 30 mPa·s (example 9), 7 wt %, 25 mPa·s(example 10), and 8 wt %, 25 mPa·s (example 11). Here, in all examples,solution viscosity is set to a value smaller than 35 mPa·s.

Here, the film thickness of the alignment film material at the portionwhere the film thickness assumes the film thickness “a”, the portionwhere the film thickness assumes the film thickness “b” and the portionwhere the film thickness assumes the film thickness “c” is described forthe above-mentioned respective examples 9 to 11 in the table shown inFIG. 8 (item: after radiation of light). As can be clearly understoodfrom this table, in all embodiments, the film thickness of the alignmentfilm ORI1 on the upper surface of the thin film transistor TFT can beset to a value of not more than 30 nm. That is, the film thickness ofthe alignment film ORI1 on the upper surface of the thin film transistorTFT is set to 21 nm in the example 9, 18 nm in the example 10, and 14 nmin the example 11. On the other hand, the film thickness of thealignment film ORI1 in other region except for the upper surface of thethin film transistor TFT (the region above the pixel electrode PX) isset to 110 nm in the example 9, 100 nm in the example 10, and 110 nm inthe example 11.

Further, the film thickness of the alignment film ORI2 on the countersubstrate side is set, at a portion in FIG. 7 where the film thicknessassumes the film thickness “c”, to 110 nm in the example 9, 100 nm inthe example 10, and 110 nm in the example 11, while the film thicknessof the alignment film ORI2 assumes a value which is approximately zeroon the top surface of the pillar-shaped spacer PS although not shown inFIG. 8.

In FIG. 8, for a comparison purpose, comparison examples 7 to 9 are alsodescribed. FIG. 8 shows a case where solution concentration and solutionviscosity of the alignment film material are respectively set to 6 wt %,50 mPa·s (comparison example 7), 5 wt %, 45 mPa·s (comparison example8), and 6 wt %, 40 mPa·s (comparison example 9). In the table shown inFIG. 8, the film thickness of the alignment film before radiation oflight and the film thickness of the alignment film after radiation oflight are described in association with the above-mentioned examples.Here, it is found that the film thickness of the alignment film ORI1 onthe top surface of the spacer pedestal SS becomes larger than 30 nm.

<Comparison Example 10>

FIG. 9 shows the constitution in which a spacer pedestal (or a partwhich replaces the spacer pedestal such as the above-mentioned thin filmtransistor TFT) is not provided at a position which faces apillar-shaped spacer PS. That is, FIG. 9 shows a comparison examplewhich facilitates the understanding of advantageous effects of theabove-mentioned respective examples in terms of quantity.

FIG. 9 corresponds to FIG. 1, and shows the constitution where thepillar-shaped spacer PS on a counter substrate side faces an alignmentfilm ORI1 on an electrode substrate at an intersecting position of agate signal line GL and a drain signal line DL.

In this case, a manufacturing method of the alignment film ORI1 issubstantially equal to the manufacturing method of the alignment filmORI1 explained in conjunction with the embodiment 1, wherein solutionconcentration and solution viscosity of an alignment film material areset to 7 wt % and 30 mPa·s, for example, as shown in FIG. 10. Further,in a table shown in FIG. 10, a film thickness of the alignment filmmaterial at positions where the film thickness is set to a filmthickness “a”, a film thickness “b” and a film thickness “c” in FIG. 9is described with respect to a case before radiation of light and a caseafter radiation of light respectively. In this case, the film thickness“b” of the alignment film ORI1 which faces the pillar-shaped spacer PSafter the radiation of light becomes 100 nm so that the film thickness“b” of the alignment film ORI1 largely exceeds 30 nm.

That is, on a liquid-crystal-layer-LC-side surface of the electrodesubstrate which faces the pillar-shaped spacer PS in an opposed manner,the liquid-crystal-layer-LC-side surface of the electrode substrate isonly 300 nm which is a film thickness of the gate signal line GL, andthe alignment film ORI1 is brought into contact with the top surfaceover an area larger than an area of the top surface of the pillar-shapedspacer PS and hence, the film thickness “b” of the alignment film ORI1is largely increased to 100 nm even after the radiation of light.

FIG. 11 shows a result of inspection of respectivebright-spot-generation withstand voltage levels with respect to theexamples 1 to 4, the comparison examples 1 to 3, the examples 5 to 8,the comparison examples 4 to 6, examples 9 to 11, and the comparisonexamples 7 to 10.

FIG. 11 shows the respective bright-spot-generation withstand voltagelevels with respect to the film thickness “b” of the alignment filmwhich faces the pillar-shaped spacer PS after radiation of light in therespective examples and the respective comparison examples.

Here, the bright-spot-generation withstand voltage level is classifiedinto 7 stages consisting of 0 to 6. As shown in FIG. 12, thebright-spot-generation withstand voltage level is evaluated based on thepresence or the non-presence of the generation of bright spots at thetime of completion of the liquid crystal display device, the presence orthe non-presence of the abrasion of the surface alignment film at thetime of disassembling the liquid crystal display device, the presence orthe non-presence of the generation of bright spots after a vibrationtest (3G), the presence or the non-presence of the abrasion of thesurface alignment film after the vibration test (3G), the presence orthe non-presence of generation of bright spots after a vibration test(5G), and the presence or the non-presence of the abrasion of thesurface alignment film after the vibration test (5G). Here, with respectto the abrasion of the surface alignment film, there exists apossibility that even when the abrasion of the surface alignment film isnot found in the observation carried out immediately after the test, anabraded portion which is concealed by a light blocking portion (a blackmatrix or the like, for example) appears on a display area due to achange with time and hence, such abrasion is also subject to theevaluation.

FIG. 13 is a graph converted from the table shown in FIG. 11, wherein analignment film thickness (nm) is taken on an abscissa, and thebright-spot-generation withstand voltage level is taken on an ordinate.An allowable range is set such that it is sufficient for a liquidcrystal display device that no abrasion of the surface alignment filmoccurs in the vibration test (3G) and a liquid crystal display devicewhose bright-spot-generation withstand voltage level is up to 2 isrendered acceptable. In this case, it is understood that the filmthickness “b” of the alignment film which faces the pillar-shaped spacerPS after the radiation of light is set to a value of not more than 30nm.

What is claimed is:
 1. A liquid crystal display device comprising: afirst substrate; a first alignment film formed over the first substrate;a second substrate; a second alignment film formed over the secondsubstrate; a liquid crystal layer sandwiched between the first alignmentfilm and the second alignment film; a projecting portion formed over thesecond substrate; a first electrode and a second electrode formedbetween the first alignment film and the first substrate; and aninsulation film disposed between the second electrode and the liquidcrystal layer; wherein the first electrode is covered by the firstalignment film; wherein the insulation film is covered by the firstalignment film; wherein the liquid crystal layer is controlled by anelectric field generated between the first electrode and the secondelectrode; wherein the first alignment film is a photo alignment film;and wherein a thickness “d2” of the second alignment film over theprojecting portion and a film thickness “d1” of a portion of the firstalignment film facing the projecting portion satisfy formula (1) and(2):0 nm<d2<30 nm  (1);d2<d1  (2).
 2. A liquid crystal display device according to claim 1,wherein the second electrode is a planar electrode, and the firstelectrode is a linear electrode which is disposed between the secondelectrode and the liquid crystal layer.
 3. A liquid crystal displaydevice according to claim 1, further comprising a small projectiondisposed between the projecting portion and the first substrate; whereinthe small projection has a height smaller than a height of theprojecting portion, and the film thickness “d1” of the first alignmentfilm is provided over the small projection.
 4. A liquid crystal displaydevice comprising: a first substrate; a first alignment film formed overthe first substrate; a second substrate; a second alignment film formedover the second substrate; a liquid crystal layer sandwiched between thefirst alignment film and the second alignment film; a projecting portionformed over the second substrate; a first electrode and a secondelectrode formed between the first alignment film and the firstsubstrate; and an insulation film disposed between the second electrodeand the liquid crystal layer; wherein the first electrode is covered bythe first alignment film; wherein the insulation film is covered by thefirst alignment film; wherein the liquid crystal layer is controlled byan electric field generated between the first electrode and the secondelectrode; wherein the second alignment film is a photo alignment film;and wherein a film thickness “d2” of the second alignment film over theprojecting portion and a film thickness “d1” of a portion of the firstalignment film facing the projecting portion satisfy formula (1) andformula (2):0 nm<d2<30 nm  (1);d2<d1  (2).
 5. A liquid crystal display device according to claim 4,wherein the second electrode is a planar electrode, and the firstelectrode is a linear electrode which is disposed between the secondelectrode and the liquid crystal layer.
 6. A liquid crystal displaydevice according to claim 4, further comprising a small projectiondisposed between the projecting portion and the first substrate; whereinthe small projection has a height smaller than a height of theprojecting portion, and the film thickness “d1” of the first alignmentfilm is provided over the small projection.
 7. A liquid crystal displaydevice according to claim 1, wherein the first alignment film is formedfrom a material having a skeleton of cyclobutane tetracarboxylic acid.8. A liquid crystal display device according to claim 3, furthercomprising: a gate line, a thin film transistor, and a stacked structureconstituted of a semiconductor layer and a metal layer; wherein the gateline overlaps with the thin film transistor and the stacked structure;and wherein the small projection includes the stacked structure.
 9. Aliquid crystal display device according to claim 4, wherein the firstalignment film formed from a material having a skeleton of cyclobutanetetracarboxylic acid.
 10. A liquid crystal display device according toclaim 6, further comprising; a gate line, a thin film transistor, and astacked structure constituted of a semiconductor layer and a metallayer; wherein the gate line overlaps with the thin film transistor andthe stacked structure; and wherein the small projection includes thestacked structure.